1. Field of the Invention
The invention relates to a gangway for movement of individuals between a dock and a boat, and, more particularly, to such a gangway having provisions allowing for variations in the vertical distance between the boat deck and the dock and additionally having provisions for changes in the configuration of the gangway to accommodate different docks.
2. Summary of the Background Art
Since ancient times, people have devised numerous devices, generally known as gangways or gangplanks, to facilitate the movement of individuals between docks and boat decks. A simple device for this purpose is a plank or ramp, wide enough to walk safely along, extending upward or downward to the deck of a ship from the dock. However, a problem with such a simple solution quickly arises from the magnitude of the vertical distance between the dock surface and the boat deck and because of variations occurring in this distance. Such variations may occur slowly, with changes in tidal levels, or very rapidly, as with waves caused by passing boats. A ramp to be used in a conventional manner, i.e. walking, not crawling or climbing up and down, for pedestrian traffic should not have a slope steeper than about fifteen degrees. Fulfilling this requirement, together with the requirement to provide for the magnitude and changes in the vertical distance between a dock and a boat deck often results in a ramp that is much too long to use in a number of docking situations. Furthermore, even when such a long ramp can be accommodated on the dock, it is often too bulky and heavy for easy movement and storage.
Much steeper angles are easily handled by providing steps, in the form of a stairway, instead of a ramp. However, since a stairway is easily used only when its individual steps are nearly level, the inclination of a conventional stairway cannot be used to compensate for significant changes in the vertical distance between the dock surface and the deck height. Compensation for such changes is needed if the gangway is to be used on a particular boat with a number of different docks, on a particular dock with a number of different boats, or, in many instances in a particular application under conditions of tidal changes and waves from passing boats.
One solution for this problem is to provide a stairway with pivotable steps and with a linkage causing the steps to pivot with changes in the inclination of the stairway so that the steps remain level. Stairways of this kind are described, for example, in U.S. Pat. Nos. 5,657,832, 5,794,292, and 5,950,267. However, the mechanism required for providing this function tends to make the stairways complex, heavy, and therefore difficult to move. Furthermore, unless pinch points in the mechanism are avoided, injury can result from becoming caught between parts moving rapidly and with great force when the boat to which the stairway is attached moves up and down with waves from a passing boat. In this regard, U.S. Pat. No. 5,794,292 describes a method for reducing the effects of pinch points between adjacent steps. Thus, what is needed is a method allowing the use of a simple ramp, not having steps, to accommodate relatively small variations in the vertical distance between a deck and a dock, together with another means to accommodate larger, slowly occurring changes in such a distance.
Another way to provide additional flexibility in the configuration of a gangway is to provide an articulated structure, with two or more sections pivotally connected. Such sections may include ramps and/or stairways. Examples of such articulated structures are described in U.S. Pat. Nos. 4,133,067, 4,366,591, 4,998,313, and 5,224,437. However, the flexibility of such structures is still limited by fact that the sections are connected in a way allowing only pivotal motion, and by the practical limitations on variations in the inclination of the individual sections. What is needed is an articulated structure having additional flexibility in the way its sections are connected, so that such flexibility can be used to accommodate large variations in the vertical distance between the dock surface and the boat deck, while changes in the inclination of a portion of the structure, such as a ramp are used to accommodate smaller, rapidly-occurring changes in this vertical distance.
In accordance with the present invention, a gangway includes a ramp configured for placement on a dock and a ladder provided with means for attachment to the deck of a boat. The ladder includes a number of steps and a number of corresponding attachment locations from which the ramp may be pivoted.
Apparatus used to board a boat should provide for safe and convenient movement in both directions between a dock and the deck of the boat, in spite of variations in the level of the boat. For example, some of such variations occur slowly, with the tidal level of the water in which the boat is floating or with seasonal variations in the water level of a lake, while others of such variations occur rapidly, as the boat is moved by the wake of a passing vessel.
In the present invention, the slowly occurring variations are accommodated by providing a number of locations at which the ramp can be attached to the ladder and by pivotally attaching the ramp to the ladder. While changes in the slope of the ramp perform part of this accommodation, different attachment locations can be used to limit the slope to one that can be easily traversed. Rapid changes in the level of the boat are also accommodated by the pivoting of the ramp on the ladder. Since only this pivoting motion occurs with rapid changes in the water level, pinch points, which could otherwise cause injuries, are avoided.